In the manufacturing and selling of integrated circuit devices, it is common to test integrated circuit dice while still part of a semiconductor wafer and mark or map the dice that perform properly, then dice the wafer into chips and discard the unacceptable dice.
Most integrated circuit devices are advertised as operating at a given speed. These devices are available in only one speed grade (unless older devices at a lower speed grade are still available). During manufacturing, if an acceptable speed is not achieved, the die is marked as bad and discarded.
However, some products, such as FPGAs, are offered in multiple speed grades, and the higher speed grades are sold at higher prices. It is desirable from the point of view of such a manufacturer to sell each device at the highest possible price while meeting the advertised speed grade.
Customers who buy integrated circuit devices available at several speed grades typically want them in a particular kind of package and want them to operate at a selected speed. In the past, when a customer orders parts and specifies the package and speed grade, the dice that have been tested and found good are packaged into the desired package, then tested for speed. Typically, some of the dice will prove to be faster than ordered, some will be the speed ordered, and some will be too slow to be acceptable. Those that are too slow will not be sold to the customer. Sometimes if insufficient inventory is available at the speed grade ordered, the manufacturer may fill an order using devices having a higher speed grade than ordered, but at the lower price.
FIG. 1 shows a conventional process for testing, packaging, and shipping integrated circuit devices. Starting from the completely manufactured integrated circuit wafer, during wafer sort process 100, at step 101 the wafer is tested to identify good and bad dice. At step 102, while the dice on the wafer are being tested, a map is made of which dice meet each speed grade. At step 103, bad dice may be inked, or otherwise designated for later discarding.
At step 104 the wafer is sawed or diced to separate the dice from each other.
During the die attach and bonding process 105, at step 106, the good dice are picked and each is attached to a pre-selected package type. However, in the past, the speed grade of each die is not retained. At step 107, bad dice are discarded.
At step 108, the good dice are wire bonded to pins in the package. At step 109, the die with its wire bonds is encapsulated to complete the package, and at step 110, the package receives initial marking, such as the name of the company, the part number, the package type, and other available information. It may also be marked with a particular speed grade, especially if the wafer was found to include predominantly one speed grade. However, with some equipment, information about the speed grade of the particular die has been lost during this handling process.
At step 111, an electrical test for proper functioning also includes a test for speed grade.
At step 112, if the die is still good after packaging, it may be marked with the speed grade if speed grade was not marked earlier. If there is an outstanding order for this package with this speed grade, at step 113, devices meeting these requirements are shipped to the customer. If there is insufficient inventory to meet the order, devices having a higher speed grade may be re-marked to the lower speed grade and also shipped to complete the order. At step 114, devices having other speed grades or devices not yet ordered are stored as finished goods in speed bins according to their speed grades.
Thus, the past method results in two inefficiencies: dice that are faster than ordered do not always sell at their highest price, plus they incur a re-marking expense, and dice that are slower than ordered are often packaged and stored as inventory for an extended period, and may even be discarded.
It is desirable to develop a test method and equipment that will improve efficiency over the present test methods and equipment.